PROJECT SUMMARY

Agriculture is facing the crucial challenge of adapting crop productivity to changes in the climate. The BBSRC BRAVO project brings together UK plant scientists and industries representing horticultural and oilseed Brassica crops to increase robustness in crop performance, combatting environmental change. Brassica species contain a wealth of natural variation that can be exploited to improve crops. BRAVO will use this variation to understand the gene networks controlling flowering time and study how these networks affect all developmental stages, from vegetative growth to seed production. Determining relationships between genes, traits and the environment will aid targeted crop improvement to secure future yields.

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DETAIL

Rothamsted Research mainly contributes to two Work Packages within BRAVO, which is led by the John Innes Centre (JIC).

Work Package 4: Gametophyte-to-sporophyte: Exploiting knowledge of trade-offs between seed size and number to maximise seed yield.

Seed size, number and oil content are the ultimate determinants of profitability for farmers growing Brassica napus in the UK. Both size and oil content also have ancillary effects on the early stages of crop establishment through their contribution to seedling vigour. Domestication of many crops has been accompanied by an increase in the relative size of the harvested organ, but this has not (yet) been the case for oilseed rape. Here, breeding effort has focused on improving composition (e.g. canola/ ‘double zero’ varieties), overall yield and uniformity, with associated agronomic traits such as disease resistance and reduced lodging. Discussions with oilseed rape breeders indicate that increases in seed size would be desirable as long as seed number is retained. The concern voiced by crop physiologists is that overall seed size and yield are constrained by source-sink relationships (the seed yield trade-off paradigm), although these have not been assigned to the various constituent compartments (vegetative tissue, silique, seed coat, endosperm, embryo etc.).

Larger seeds can result in increased yield of the economic product (oil), for example in oilseeds by reducing the seed coat-to-embryo ratio. During early development of siliques (gynoecia), initiation of ovule primordia is a limiting factor determining the final seed number per silique. The number of ovules generated in B. napus is usually greater than the final seed number per pod. Genetic variation in the number of ovules per silique (and therefore seed number per silique) has been observed in Arabidopsis. We hypothesise that harnessing genetic variation in this trait is of key importance in optimising seed number per silique, and therefore seed yield.

The information we obtain will assist plant breeders and biologists in developing methods to select material from the Brassica gene pool with which to predictably change seed size and number, and potentially decouple these two key yield factors to defeat the trade-off paradigm.

Seed vigour is the product of interactions between multiple seed tissues and the environment during seed set, which is sensed and transduced via flowering time pathways. Variation in seed vigour is caused by variation in weather during seed set, and is an intensifying climate-change threat to UK agriculture. Attempts to compensate for this phenomenon can lead to yield reductions via accidental under- and over-sowing by farmers. Our stakeholder meetings have revealed demands for a greater reliability of seed vigour, from both growers and seed companies. This seed performance variation is driven in part by networks of flowering time genes active in fruit and seed tissues and is common to all angiosperms.

Poor seed vigour also leads to reduced efficiency in vegetable Brassica production, as all plants for the UK market must currently be raised in plugs under controlled conditions. This was previously the case for lettuce, but new varieties and improved seed technology now mean that direct drilling of lettuce seed is being trialled in the UK for the first time. We hypothesise that this is also possible for Brassica oleracea.

This work package will address the improvement of seed vigour in B. oleracea and B. napus and elimination of variation in seedling establishment caused by environmental variation during seed production.